Lidar (light detection and ranging) uses laser technology to make precise distance measurements over long or short distances. One application of lidar is the range scanner, or scanning lidar. Lidar transceivers operate on the principle of transmitting laser light that then reflects off of a given object and returns to a lidar receiver. The distance to an object is then determined by analyzing the laser signal through various techniques. During the scanning process, the lidar makes repeated range measurements to objects in its path. Many LIDAR units reflect a pulsed beam of laser light from a rotating mirror to scan across the angular range of the unit (i.e., the “field of view”) in a fan-like pattern. The range measurements are thus aligned along a singular angular dimension. Acquiring truly three-dimensional measurements has traditionally required either movement of the laser scanner unit as a whole or more complex actuation of the mirror reflecting the pulsed laser beam, such as scanning in a second angular dimension. Each of these approaches increases the cost of the unit and increases the amount of time required to scan a region of interest.
Three-dimensional laser scanning is relatively commonplace, finding widespread application in industrial design, architecture, civil engineering, military operations, and scientific research. In most systems, the scanner scans its entire field of view one point at a time by changing the rangefinder's direction of view to scan different points. The view direction of the laser rangefinder can be changed by either rotating the rangefinder itself, or by using a system of rotating mirrors. Typically, the entire range of one angular dimension is scanned before the beam is advanced along the other angular dimension. A full scan is thus a time-consuming process. Similarly, some existing systems use a mirror to guide a standard LIDAR beam spread (along a single angular dimension) to a object. For example, in aircraft that use high-powered LIDAR systems for ground scanning, the LIDAR device typically does not move. Instead, a steerable mirror directs the beam to the desired ground region. Similarly, some LIDAR systems use a secondary mirror to steer the beam in the azimuth to allow scanning across an additional dimension.
Despite having found increasingly widespread application in research and industrial applications, scanning LIDAR units remain expensive. LIDAR units typically use a rotating mirror to both emit the laser pulses and receive the reflected light used in the range finding calculations. A particular LIDAR unit is characterized by a fixed angular range, across which the rotating mirror reflects outgoing beams and receives incoming reflections. As increasing the angular range of a unit incurs little or no additional cost, typical modern devices have relatively large angular ranges, from 180 to 270 degrees. However, in many applications, such as those in which objects or portions of an object may be occluded, multiple units (possibly with smaller viewing angles) would be preferred to a single LIDAR unit with a large viewing angle. In such applications, the system cost may become prohibitive. In addition, the operation of multiple units presents significant synchronization challenges.